1. Field of the Invention
The invention concerns a controller for a hydrostatic traversing mechanism.
Hydrostatic traversing mechanisms, in which two hydraulic motors are connected to a hydraulic pump and the hydraulic pump is driven by a driving motor, are known as traversing mechanisms of working machines such as road rollers. In such a system, in which one hydraulic motor each is assigned to the front and rear axles, to adapt the torque distribution of the individual motors to the conditions of use, e.g. uphill and downhill, various systems for traction control are known.
2. Discussion of the Prior Art
In DE 101 01 748 A1, for instance, a system in which signals from pressure sensors, which are arranged in the pressure-side and induction-side main duct, are fed to an electronic control unit, is proposed. On the basis of changes of the pressure signals and changes of the position of a driving lever, the electronic control unit determines the present driving situation of the vehicle. For this purpose, a threshold value which is corrected depending on changes of the position of the driving lever is used, so that different driving situations can be clearly distinguished from each other. If one of the pressure sensors determines a pressure value which exceeds the corrected threshold value, the driving situation which the electronic control unit determines is used to send an electrical signal for adjustment towards a lower absorption volume to an adjustment device of the up-side hydraulic motor.
The system which is proposed in DE 101 01 748 A1 has the disadvantage that the cost of construction is relatively great. Thus not only are pressure sensors required in both main ducts, but also an electronic controller, which is capable of storing changes of the position of the driving lever at least for a short time, so that it can not only evaluate an instantaneous actual value, but also include the change of the driving lever position in the determination of the driving situation.
Also, from DE 196 38 421 A1 a traction controller, in which a gradient sensor is used to prevent an unwanted adjustment of a down-side hydraulic motor in the direction of smaller pivoting angles, is known. The system is based on a traction controller, which detects differing wheel circumference speeds on the front and rear axles on the basis of r.p.m. sensors, and by adjusting the absorption volume adjusts the r.p.m. of the corresponding hydraulic motor. In this case the situation which can occur is that the wheel circumference speed of the down-side axle during downhill motion is less than the wheel circumference speed of the up-side axle, because of the slip which occurs. Because of the regulating intervention of the traction controller, this would result in an adjustment of the down-side hydraulic motor in the direction of a smaller pivoting angle, to raise the r.p.m. of the hydraulic motor, which however causes a reduction of the moment. To maintain the braking moment during downhill motion, the information of a gradient sensor is used, to suppress the control commands which the traction controller gives to the adjustment device of the hydraulic motor and thus to prevent the adjustment of the hydraulic motor in the direction of a smaller pivoting angle. The gradient sensor therefore prevents an adjustment of the pivoting angle of the hydraulic motor.
The system which is known from DE 196 38 421 A1 has the disadvantage that the traction controller intervenes only when a slip has already occurred. On the other hand, reduction of the transmitted torque to one of the axles before a slip occurs on one of the axles is not provided.